1. Field of the Invention
The present invention relates to a swash plate type compressor used for vehicular air conditioning. More particularly, it relates to an improvement of a mechanism for a rotary shaft of the compressor.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 3-92587 discloses a conventional swash plate type compressor. As shown in FIG. 11, this compressor described in the above-described publication includes a pair of opposed cylinder blocks 100 and 101. A plurality of cylinder bores 102 and 103 are formed within the cylinder blocks 100 and 101 (only one pair shown). Cylinder bores 102 and 103 are equiangularly disposed around a rotary shaft 105 which supports a swash plate 104. Double headed pistons 106 are accommodated in the paired cylinder bores 102 and 103. Compression chambers 107 and 108 are defined at the side surfaces of the piston 106, respectively. The compression chambers 107 and 108 communicate with discharge chambers 109 and 110, via discharge ports 113 and 114, respectively. Discharge valves 117 and 118 open or close the associate discharge ports 113 and 114, respectively. When the piston 106 is in the compression stroke, refrigerant gas in the compression chambers urges the discharge valves 117 and 118 away, so as to be discharged into the discharge chambers 109 and 110.
The compression chambers 107 and 108 communicate with suction chambers 111 and 112, via suction ports 115 and 116, respectively. Suction valves 119 and 120 open or close the associated suction ports 115 and 116, respectively. When the piston 106 is in the suction stroke, the refrigerant gas in the suction chambers 111 and 112 is sucked into the compression chambers 107 and 108 while the gas is urging the suction valves 119 and 120 away.
The rotary shaft 105 is supported by means of the paired cylinder blocks 100 and 101, via a pair of radial bearings 121 and 122, respectively. A pair of thrust bearings 123 and 124 are disposed between the swash plate 104 and cylinder block 100, and between the swash plate 104 and the cylinder block 101, in such a manner that the swash plate 104 is clamped by the bearings 123 and 124. Therefore, radial load acting on the shaft 105 is received by the cylinder blocks 100 and 101, via the radial bearings 121 and 122. Thrust load acting on the shaft 105 is received by the cylinder blocks 100 and 101, via the bearings 123 and 124.
When the compressor is provided with five pistons, the thrust load acting on the rotary shaft varies along a curve CU0 shown in FIG. 12. A maximum value Fmax and a minimum value negative Fmax will appear five times each while the shaft makes one revolution. In other words, the thrust load acts five times forwardly and five times rearwardly with respect to the swash plate. The shaft 105 and cylinder blocks 100 and 101 are designed with tolerances. The direction conversion of the thrust load generates lash along the shaft 105, causing noise and vibration.
However, as the pair of cylinder blocks 100 and 101 are connected, a pair of races clamping the rollers of the thrust bearings 123 and 124 are deflected beforehand. The force originated in this deformation acts as a preload on the shaft 105. The magnitude of deformation is designed so that the resultant preload exceeds the maximum value. As the magnitude of preload is determined in this manner, the generation of lash is eliminated, resulting in a successful suppression of the noise and vibration.
However, the support mechanism of the above rotary shaft includes the radial bearings 121 and 122, and thrust bearings 123 and 124, which are disposed at separate positions, and which receive the radial and thrust loads both applied on the shaft 105. This complicates the operational steps of assembling the compressor.
There is a type of compressor having a rotary shaft made of steel iron, and cylinder blocks made of aluminum to lighten the weight. The above rotary shaft support mechanism employed in this compressor causes the thermal expansion coefficient of cylinder blocks different from that of rotary shaft. Therefore, the magnitude deviation in the thermal expansion between the cylinder blocks and rotary shaft is generated due to the temperature variation of discharged refrigerant gas. Consequently, the relative connected condition between the cylinder blocks and rotary shaft varies. As a result, the undesirable preload is applied on the rotary shaft.
More specifically, the temperature of the compressor increases according to the temperature of discharged refrigerant gas when the compressor is operated in the state of high compression ratio. Therefore, the magnitude of thermal expansion of cylinder blocks, and front and rear housings along the thrust direction becomes larger than that of the rotary shaft along the same direction. Accordingly, the compressor has a high compression ratio, resulting in the largest thrust load applied on the rotary shaft. However, the preload becomes smaller than that of thrust load. Resultingly, lash is generated along the rotary shaft. There will be new drawbacks in which the noise and vibration are generated.
According to the light weight compressor, a preload will be set rather large with consideration of thermal influence. When the compressor is operated with a low compression ratio, the temperature of discharged refrigerant gas is low. The internal temperature of compression chambers is thus low. Therefore, the thermal expansion along the thrust direction of the cylinder blocks, and front and rear housings is small. Accordingly, the preload applied to the rotary shaft is large. As a result, there is a drawback in which the power loss is increased when the rotary shaft is to be rotated.